Why do manufactures recommend/require the "w" and not leave it as optional?

Correct me if I am wrong, but 5W is spec'd to -22F. Thats pretty cold, but there are plenty of places in USA that get colder occasionally.

0W is spec'd -40F. Not many get that cold, but if you want to test with one oil and put one oil in the manual?
-22°F for 5W oils (on paper), however I wouldn't start my car (and that's what specialist say) if the temp. is below -4°F.

For 0W is -30°F on paper. I bet it's not healthy for your engine to start it below -15°F.
 
-22°F for 5W oils (on paper), however I wouldn't start my car (and that's what specialist say) if the temp. is below -4°F.

For 0W is -30°F on paper. I bet it's not healthy for your engine to start it below -15°F.
But as you note there is no guarantee that an oil with a 0W winter rating will be thinner than an oil with a 5W rating until you are down to -30 or so. Above that they can be thicker. All oils are very thick at cold temperatures and it's much more about pumpability than viscosity.
 
But as you note there is no guarantee that an oil with a 0W winter rating will be thinner than an oil with a 5W rating until you are down to -30 or so. Above that they can be thicker. All oils are very thick at cold temperatures and it's much more about pumpability than viscosity.
It might be.
However, from what I've seen here at -4°F - 0W flows from the bottle the same way as, let's say, at 32°F.
And 5W looks is thicker at that temp.

So, what you are saying is that an oil gets certain viscosity at certain temp. and there is no gradual thickening or thinning with dropping or raising temp.? Hence, oil viscosity and ambient temp. are not proportional?
 
It might be.
However, from what I've seen here at -4°F - 0W flows from the bottle the same way as, let's say, at 32°F.
And 5W looks is thicker at that temp.

So, what you are saying is that an oil gets certain viscosity at certain temp. and there is no gradual thickening or thinning with dropping or raising temp.? Hence, oil viscosity and ambient temp. are not proportional?
Correct, the temperature and viscosity relationship can certainly be a curve, not a straight line.
 
Suit wearing business shirt guys
Used to be me. You don't wash shirts, you drop them off at the dry cleaner for launder and press. You need 10, drop 5 off, pick 5 up.

If you have a house full of kids you consolidate everyone's clothes then you have a load of whites (almost). Back in the day of housewives. We are 4 and everyone does there own.
 
Always lots of questions about the specifications by manufacturers.

Why do they see the need to stress one "w" over another? 0w or 5w for example

Could/should they just use "x" and leave it up to the users to decide based on location? Xw-16?

So many folks get hung up on the manufacturers recommendation and worry about warranty...which I understand.

Conceptual question about "why" stress a certain "w"...not about the virtues of the "w"
The more complicated the specifics are, the more fodder for lawyers there is. Specify one weight oil and let the owners sort it out.

Any aggrieved owners that wants to argue can argue with a lawyer in a courtroom…or arbiter in an arbitration hearing.
 
It might be.
However, from what I've seen here at -4°F - 0W flows from the bottle the same way as, let's say, at 32°F.
And 5W looks is thicker at that temp.

So, what you are saying is that an oil gets certain viscosity at certain temp. and there is no gradual thickening or thinning with dropping or raising temp.? Hence, oil viscosity and ambient temp. are not proportional?
The eye viscometer is notoriously inaccurate.
 
-22°F for 5W oils (on paper), however I wouldn't start my car (and that's what specialist say) if the temp. is below -4°F.

For 0W is -30°F on paper. I bet it's not healthy for your engine to start it below -15°F.
If that were true, cars in Edmonton and Winnipeg would have dramatically shorter lifespans, not to mention Fairbanks and anywhere else in Alaska. I've seen nothing that would indicate that there's a statistically significant difference in engine life for vehicles that are, for almost half the year, often started in temperatures that can be below -30, often -40C.
 
It might be.
However, from what I've seen here at -4°F - 0W flows from the bottle the same way as, let's say, at 32°F.
And 5W looks is thicker at that temp.

So, what you are saying is that an oil gets certain viscosity at certain temp. and there is no gradual thickening or thinning with dropping or raising temp.? Hence, oil viscosity and ambient temp. are not proportional?
The behavior of wax crystals result in a massive, and very quick, increase in viscosity, once they start to form. The purpose of PPD's in non-PAO base oils is to delay the formation of those wax crystals, allowing the oil to flow at lower temperatures. Once the point is reached where PPD's are no longer effective, you hit what is basically a viscosity "wall", where it goes from flowing to a gel that doesn't flow. PPD's also degrade in service, which is why oils are permitted to slip a Winter grade during service. So a 5W-30 that starts out passing MRV at -35C may no longer do so with 500 hours on it.

This is where PAO shines, as it has no wax, so its behaviour is very predictable at low temperatures, it doesn't hit that same wall, it just progressively gets thicker and thicker.
 
When would I ever get a full load of “whites” with my big modern washer?
This is going to blow your mind: your washing machine has a setting for load size.
When would anyone? Suit wearing business shirt guys? Doctors lab coats? Not me!
Yep, I was right, single dudes on a motor oil forum.

I tend to use bleach in my loads of white t-shirts and the wife's whites.
 
Always lots of questions about the specifications by manufacturers.

Why do they see the need to stress one "w" over another? 0w or 5w for example

Could/should they just use "x" and leave it up to the users to decide based on location? Xw-16?
The owner still has the power to use whatever viscosity they want. Most car manufacturers are going to recommend a 0W or 5W just because they want good cold weather cranking, start-up and pumpability of the oil to protect the engine. Any multi-viscosity oil in the 8, 16 KV100 grades, and many with a 20 KV100 grade are going to be a 0W.
 
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